1. Field of the Invention
This invention relates to automatic garage door operators, and more particularly to electric motors used in chaindrive door openers.
2. Description of the Prior Art
Garage door operators are well known and are commonly used to automatically open and close upwardly acting overhead garage doors. These garage door operators, which are driven by electric motors and which are usually remotely operated by radio control, provide considerable convenience to the motorist for powered, remote opening and closing of garage doors.
Garage doors are very heavy, and although garage doors are typically balanced by torsion or helical springs, the springs may not be capable of proper adjustment to adequately balance the door. In addition, some people do not keep their garage door in top-notch operating condition by lubricating it or adjusting it monthly, and garage doors may be difficult to move because of this improper adjustment or lack of lubrication. Some users will operate the door for years without paying any attention to it and will only examine the door when the operator has completely failed to operate. In fact, some people have been known to buy a door operator only when the door has become so hard to move that they can no longer move the door easily manually, and then to install a door operator instead of adjusting or lubricating the door. As a result, the commercial door operator requires a relatively powerful motor to accomplish its purpose. In addition, the operator must be powerful enough to close the door firmly, even pushing through a small amount of snow or leaves that may accumulate at the bottom of the doorway.
Of course, in order to provide a more powerful electric motor, it is usually necessary to provide a larger motor, and this increases the cost of the door operator. Therefore, it is highly desirable to increase the power of the electric motors in door operators to the greatest extent possible without changing to a larger motor.
In chain drive garage door operators, as opposed to screw drive operators, the motor is not subjected to substantial axial loading. Therefore, the bearing assembly within the motor in chain drive garage door operators has conventionally been a series of plastic thrust washers. Thrust bearings that may be necessary in applications, such as screw drive garage door operators, in which substantial axial loading is present have heretofore though to be unnecessary in the chain drive garage door operator arrangement.
In addition, because the motor shaft in chain drive garage door operators is not subjected to substantial axial loading, the shaft conventionally has been axially fixed in place, with the rotor fixed in place with respect to the stator. In this manner, it was believed, the rotor could be placed in its optimal position and would not move from that position.